The present invention relates to a carriage positioning system. The invention is particularly useful in a system for positioning a carriage along either the X- or Y-axis, and is therefore described below particularly with respect to such a system.
Two-axis carriage positioning systems are widely used in a number of applications where orthogonal positioning is required, for example in data plotters for plotting curves or preparing drawings. As a rule, the carriages are driven to their specified positions by X-axis and Y-axis drive motors. Other systems are known wherein the carriages are manually driven but are coupled to shaft encoders to read-out their positions. The coupling between the respective motors or encoders and carriages is usually effected by flexible coupling elements, such as cables, belts or chains. Usually a single cable, belt or chain is trained over a plurality of pulleys for driving the X-axis carriage; and a separate cable, belt or chain is trained over another group of pulleys for driving the Y-axis carriage.
In the known systems using a single flexible coupling element (e.g., cable, belt or chain) for the X-axis carriage, the coupling element must necessarily be very long, and therefore dimensional changes in the element due to strain or temperature-variations greatly affect the precision of the system in positioning the respective carriage. In addition, the use of a single such flexible coupling element for the X-axis places a great load on the couling element which tends to increase dimensional changes due to strain, and also limits the load capability of the positioning system. Further, many of the known systems require the flexible coupling elements to change planes, and therefore, are either restricted to the use of cables, or include complicated constructions to accommodate the change in planes. Still further, the pulley arrangement in many of the known systems produce a transmission ratio or the X-axis coupling element which is not identical to that of the Y-axis coupling element, and therefore require different gearing or the like in order to accommodate or equate the different transmission ratios.